Improved bridge



@anni @time WILLIAM P; TROWBRIDGE, OF NEWTOWN,NEW YORK.

Letters Patent No. 94,529, dated September 7 1869.

IMPRO'V'ED BRIDGE.

The Schedule referred to i'n these Letters Patent and making part of the same.

To whom 'it may concern:

Be it known that I, WILLIAM P. TROWBRIDGE, of Newtown, Queens county, New York State, have invented certain new and useful Improvements in the Construction of Bridges; and I hereby declare the following to be a full, clear, and exact description of the same, reference b eing had to the accompanying drawings, in which- Figure 1 is a perspectivev view of a completed trussbridge, made in accordance with my invention.

Figure 2 is a side elevation of the same, representing the half trusses as not yet joined.

My invention is especially applicable tocases when the great length of span, the necessity of a great altitude for the bridge, and the difficulties of erecting auxiliary staging for erecting the structure, render the use of ordinary single trusses difdcult, if not impracticable, but this system may be used to advantage in any case.

l The plan which I propose may be described as folows:

Two separate and independent glider-beams or trusses, A B, are constructed on the land, at the terminus of the bridge-crossing, one `upon each bank, and in the line of the bridge, as seen in iig. 2.

The trusses'or girders are built of such strength and form, that-they may be pushed or launched out over the channel, the' projecting ends of each truss spanning one-half the channel, and meeting over the middie of the channel, as represented in g. 1.

`During the operation of pushing out, the shore-ends are loaded with temporary weights to counterbalance the prjectingpaits.

After the projecting ends are brought together, they .are permanently united in such a manner that thetwo half spans will become one 'single or continuous truss, gil-der, or beam.

The shore-ends may then be fastened with bolts or tie-rods to the piers, and the auxiliary counterweights removed.

. The masses of the piers or masonry will thus be made to act as the counterweights. v

In order to provide for the sliding of the bridge on the abutments by contraction and: expansion, rollers a, after the bridge is in place, may be. placed under the trusses, and between the trusses and piers or bed on which the trusses rest, and the rods or bolts which tie the trusses to the piers vwould also have a. sui cient adjustability to allow of this slight motion.

As regards the form of the half trusses or girders, they may be madev as indicated in the drawings, or in the form of simpletrusses or tubes, or their construction may be otherwise varied in the manner well known to those skilled in the art to which this invention pertains.

The trusses can be readily built and completed ou a level with the ground, and then raised up and placed upon the piers or masonry D, from which they are to be projected.

It will be -seen that several important points are gained by this construction:

First, each separate half truss being made to bear the greatest load that will come upon it before the two are joined, after they are joined the two will bear a greatly increased weight without deflection, by virtue of the single beam which they form, and consequently it is possible to build, for a given4 load and span, the whole truss of lighter proportions.

Second, as the overhanging half girders extendback inland, and the inner ends are fixed to the piers, iucreased strength is thereby added to the entire structure.

Third,lc0ntracti0n and expansion by heat and cold `will not, as in a simple ,suspension-budge, cause the middle ofthe spanto droop.

Fourth, it is possible to attain greater spans by this 'method than by any other, except the simple suspension-bridge, and, atthe same time, retainrthe virtue of the beam or girder-systenn as to stiffness, freedom `from vibrations, and oscillations'.

Fifth, no auxiliary staging is required for the construction,

Sixth, the half trusses may be constructed on a lower level, and then raisedup before heilig launchedout.

.Having nowdescribed my invention, and the man 1 In testimony whereof, I have signed my name to this specification, before two subscribing witnesses. W. I. TROWBRIDGE.v

Witnesses:

' HORATIO ALLEN, CHAs. E. EMERr. 

